Deactivation study of K2O/NaX and Na2O/NaX catalysts for biodiesel production

• Na2O/NaX catalyst shows activity (94% methyl esters) after several uses.
• After the first use, the methyl esters yield is high (94–98%).
• The catalytic activity lost is mainly due to leaching of active sites.
• Leaching of Na is significantly less pronounced than K.
• Acetone is a better solvent to wash the catalyst than methanol.

A performance comparison of K2O/NaX and Na2O/NaX catalysts was carried out in the safflower oil transesterification. The studied variables were three: number of cycles of use, washing between cycles and type of solvent to do the washing. Parameters specified by the European standard UNE-EN 14214 were taken as response variables. These parameters were methyl esters content, viscosity and acid value. The fresh and spent catalysts were characterized by XRD, SEM, IR, AA and Hammett Method. It was found that with both catalysts after the first use, a high methyl esters content is obtained (94% and 98% with the K2O/NaX and Na2O/NaX, respectively). However, both catalysts lose activity according to a second order deactivation law. The deactivation constant of the K2O/NaX was found to be about three times higher than that calculated for the Na2O/NaX catalyst. The deactivation was found to be mainly due to leaching of active species and catalytic surface fouling. Nevertheless, the Na2O/NaX catalyst leads to attain high methyl esters content (94–96%) very close to that specified by the aforementioned standard even after several uses. Also, viscosity and acid values of the biodiesel produced with this catalyst met the norm at all uses. Therefore, between the studied catalysts here, Na2O/NaX is the recommended one to produce biodiesel from safflower oil transesterification at a greater scale.

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